Phase-mediated cobalt phosphide with unique core-shell architecture serving as efficient and bifunctional electrocatalyst for hydrogen evolution and oxygen reduction reaction

Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) have been considered as two critical processes in the field of electrocatalytic water-splitting for hydrogen production and fuel cells. However, the sluggish reaction kinetics of HER and ORR required efficient electrocatalyst such as Pt to promote such process. Transition metal phosphides (TMPs) exhibit great potential to replace noble metal electrocatalysts to accelerate HER and ORR due to their high activity and easy availability. Herein, a highly-efficient bifunctional CoP electrocatalyst for HER and ORR, featuring a unique core-shell structure decorated on nitrogen-doped carbon matrix was designed and constructed via etching a cobalt-based zeolitic imidazolate framework (ZIF-67) with phytic acid (PA) followed by pyrolysis treatment (PA-ZIF-67–900). Experimental results revealed that the pure-phase single-crystalline CoP exhibited outstanding electrocatalytic performance in HER and ORR, superior to Co(PO₃)₂ in PA-ZIF-67–700, hybrid phase of Co(PO₃)₂ and CoP in PA-ZIF-67–800 and Co₂P-doped CoP in PA-ZIF-67–1000. To reach the current density of 10 mA/cm² the as-synthesized CoP required an overpotential of 120 mV for HER in 1 mol/L KOH and half-wave potential of 0.85 V in O₂-saturated 0.1 mol/L KOH. This work present new clue for construction of efficient and bifunctional electrocatalyst in the field of energy conversion and storage     

多壳层中空FeP微球的制备及全Ph范围的电催化产氢性能

设计合成了一种多壳层中空多孔结构的磷化铁(FeP)微球, 通过扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 X射线衍射(XRD)和X射线光电子能谱(XPS)对微球的表面形貌和物相组成等进行表征, 并通过电化学工作站测试了材料的析氢性能. 结果表明, FeP微球和掺杂导电剂碳纳米管(CNT)后的FeP/CNT复合电催化剂在宽pH范围的电解液中均展现出了优异的电催化活性, 在酸性、 碱性和中性条件下析氢反应过程中的塔菲尔斜率分别为55.0, 64.9, 163.2 mV/dec, 当电流密度达到10 mA/cm ²时, 过电势仅分别为97, 169, 495 mV(vs. RHE), 且表现出了超长的循环稳定性.     

Ultrafine molybdenum carbide nanoparticles supported on nitrogen doped carbon nanosheets for hydrogen evolution reaction

Nitrogen doped carbon nanosheets supported molybdenum carbides nanoparticles (Mo_xC/NCS) have been synthesized by tuning the mass ratio of melamine and ammonia molybdate. The Mo₂C/NCS-10 exhibits superior electrocatalytic performance and stability for HER, which was attributed to N-doped carbon nanosheets, small particle size, mesoporous structure, and large electrochemical active surface area.     

Heterostructures of NiFe LDH hierarchically assembled on MoS2 nanosheets as high-efficiency electrocatalysts for overall water splitting

Typically, rational interfacial engineering can effectively modify the adsorption energy of active hydrogen molecules to improve water splitting efficiency. NiFe layered double hydroxide (NiFe LDH) composite, an efficient oxygen evolution reaction (OER) catalyst, suffers from slow hydrogen evolution reaction (HER) kinetics, restricting its application for overall water splitting. Herein, we construct the hierarchical MoS₂/NiFe LDH nanosheets with a heterogeneous interface used for HER and OER. Benefiting the hierarchical heterogeneous interface optimized hydrogen Gibbs free energy, tens of exposed active sites, rapid mass- and charge-transfer processes, the MoS₂/NiFe LDH displays a highly efficient synergistic electrocatalytic effect. The MoS₂/NiFe LDH electrode in 1 mol/L KOH exhibits excellent HER activity, only 98 mV overpotential at 10 mA/cm². Significantly, when it assembled as anode and cathode for overall water splitting, only 1.61 V cell voltage was required to achieve 10 mA/cm² with excellent durability (50 h).     

Engineering heterostructure and crystallinity of Ru/RuS2 nanoparticle composited with N-doped graphene as electrocatalysts for alkaline hydrogen evolution

Crystalline engineering and heterostructure have attracted much attention as effective strategies to improve the electrocatalytic activity for hydrogen evolution reaction (HER). In this study, a new heterostructure catalyst (Ru/RuS₂@N-rGO) with low crystallinity was fabricated by a simple and low-temperature method for HER in alkaline solution, applying the Na₂SO₄ as S source and polypyrrole as N source. Optimizing through the controllable crystalline engineering and composition ratio of Ru and RuS₂, the Ru/RuS₂@N-rGO heterocatalyst at the calcining 500 °C revealed highly efficient HER activity with overpotential 18 mV at a current density 10 mA/cm² and remarkable stability for 24 h in 1.0 mol/L KOH. This work provides a facile and effective method in designing advanced electrocatalysts for HER in the alkaline electrolytes by synergistically structural and component modulations.     

General synthesis of Pt and Ni co-doped porous carbon nanofibers to boost HER performance in both acidic and alkaline solutions

It is essential to develop efficient electrocatalysts to generate hydrogen from water electrolysis for hydrogen economy. In this work, platinum(Pt) and nickel(Ni) co-doped porous carbon nanofibers(Pt/NiPCNFs) with low Pt content were prepared via an electrospinning, carbonization and galvanic replacement reaction. Because of the high electrical conductivity, abundant electrochemical active sites and synergistic effect between Pt and Ni nanoparticles, the optimized Pt/Ni-PCNFs catalyst shows an e...     

Imine Gels Based on Ferrocene and Porphyrin and Their Electrocatalytic Property

A series of porphyrin‐based imine gels have been synthesized via dynamic covalent gelation between 5,10,15,20‐tetra(4‐aminophenyl)‐21H,23H‐porphyrin (H₂TAPP) derivatives and various aldehyde compounds. The porphyrin‐ferrocene imine gels based on MTAPP (M=H₂, Ni²⁺, Co²⁺, Pd²⁺ and Zn²⁺) and ferrocene‐1,1′‐dicarbaldehyde (NA) display efficient HER, OER and ORR activities in alkaline media. Among the gels, CoTAPP‐NA shows an HER current density of 10 mA cm^?2 at low overpotential of 470 mV and small Tafel slope of 110 mV decade^?1 in alkaline media. CoTAPP‐NA also exhibits OER catalytic activity with low overpotential (416 mV for 10 mA cm^?2). CoTAPP‐NA shows ability in overall water splitting in alkaline media. In addition, CoTAPP‐NA exhibits onset potential (E_p) of 0.95 V and half‐wave potential (E_1/2) of 0.84 V in 1.0 mol L^?1 KOH solution for oxygen reduction. Moreover, the gel catalyst shows good stability.     

CoP/Co_2P/C纳米材料用于全pH值电催化析氢

在氮气下一步退火含有植酸和钴的前驱体,合成了一种新型的CoP/Co2P/C复合纳米材料作为电催化剂,该催化剂在全pH值范围下表现出优异的电催化析氢活性和稳定性.在0.5mol/L的硫酸中,电流密度为10mA/cm~2时,过电位为135mV.在1mol/L KOH溶液中,CoP/Co_2P/C催化剂需要141 mV的过电位才能使电流密度达到10 mA/cm~2,在0.1mol/L磷酸盐缓冲溶液中,需要155mV的过电位才能使电流密度达到10mA/cm~2.这种优异的析氢活性主要归因于CoP/Co_2P纳米粒子和C层之间的协同作用.     

Metal-organic framework derived NiCoP hollow polyhedrons electrocatalyst for pH-universal hydrogen evolution reaction

Hollow nanostructures have attracted increasing research interest in hydrogen evolution reaction owing to their unique structural features.Herein,Ni-Co mixed metal phosphide hollow and porous polyhedrons was successfully composited(expressed as NiCoP).Benefiting from the synergistic effects of ZIF-67 by doping Ni elements and the well-defined hollow and porous structure,the as-synthesized NiCoP hollow and porous polyhedrons exhibit better electrochemical properties and mechanical stability for hydrogen evolution reaction over a pH-universal range,with a small Tafel slopes of 72,101,176 mV/dec,and a low overpotential of 82,102,261 mV at a current density of 10 mA/cm² in 0.5 mol/L H₂SO₄,1 mol/L KOH and1 mol/L phosphate buffer solution(PBS).This general strategy can also be applied to fabricate other hollow cobalt-based phosphides and MOFs-derived materials for HER.     

Optimizing the electronic structure of Fe-doped Co3O4 supported Ru catalyst via metal-support interaction boosting oxygen evolution reaction and hydrogen evolution reaction

Metal-support interaction(MSI) is an efficient way in heterogeneous catalysis and electrocatalysis to modulate the electronic structure of metal for enhanced catalytic activity. However, there are still great challenges in promoting the hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) simultaneously by this way. Herein, Fe-doped Co₃O₄ supported Ru(Ru/FeCo) catalysts are synthesized by MSI strategies to further improve the electrocatalytic activity and sta...     

The influence of solution composition on the kinetics of “reduced” CO2 electrooxidation at polycrystalline platinum

The electrooxidationof “reduced” CO₂ intermediate adsorbed at polycrystalline Pt was studied for comparison in 0.5 M H₂SO₄, 0.05 M HClO₄ and 1 M KOH. The voltammograms showed a current peak multicity in 0.05 M HClO₄ and in 1 M KOH. Current transients in 0.05 M HClO₄ showed a complex decay at E_o, between 0.6 and 0.8 V. In 1 M KOH these transients showed a minimum and a maximum which shift in the time scale with E_ad.The kinetic interpretation of the results was attempted considering a Temkin isotherm at low positive potentials. Tafel slopes obtained from the dependence of E_p vs. log υ are close to RT/F at high positive potentials. This value accounts for a chemical reaction as rds. Anion Adsorption at the polycrystalline Pt electrode would change the surface energy for Pt(OH) electroformation and hence it should influence the electrooxidation processes indirectly.     

Accelerating the oxygen reduction reaction via a bioinspired carbon‐supported zinc electrocatalyst

Oxygen utilization in electrochemical energy generation systems requires to overcome the slow kinetics of oxygen reduction reaction (ORR). Herein, we have outstretched an efficient strategy in order for developing a bioinspired Zn (N₄)/sulfur/graphitic carbon composite (Zn‐S‐Gc) with an effective performance for the ORR at low temperature. The catalyst composite was created by attaching the Zn (N₄) centers in the form of zinc phthalocyanine on the sulfur‐linked graphitic carbon surface. The most positive ORR onset potential of about 1.00 V versus a reversible hydrogen electrode (RHE) was obtained due to the unique structure of a new catalyst in KOH solution (pH = 13) at low temperature (T = 298 K). The catalyst was evaluated using the rotating‐disk electrode method in the potential range of ?0.02–1.18 V versus RHE. The number of transferred electrons as one of the most important parameters (n > 3.70) is almost constant in a wide range of low overpotentials (0.1–0.6 V), which indicates a more efficient four‐electron pathway from O₂ to H₂O on the catalyst surface. The estimated Tafel slope in an appropriate range is about ≈ ?133.3 mV/dec at a low current density and E_1/2 of the electrocatalyst displays a negative shift of only 11 mV after 10,000 cycles. The mean size of the catalyst centers is on the nanoscale (<50 nm).     

Interfacial coupling of sea urchin-like (Mo4O11-MoS2-VO2) promoted electron redistributions for significantly boosted hydrogen evolution reaction

Developing efficient electrocatalysts for hydrogen evolution reaction (HER) is of great importance in contemporary water electrolysis technology. Here, a novel hierarchically sea urchin-like electrocatalyst (Mo₄O₁₁-MoS₂-VO₂) is synthesized by hydrothermal deposition and post-annealing strategy. The optimized electrocatalyst behaves as a high active hydrogen evolution electrode in 0.5 mol/L H₂SO₄. This electrode needs overpotential of only 43 mV to achieve 10 mA/cm² with a Tafel slope of 37 mV/dec and maintains its catalytic activity for at least 36 h. Better than most previously reported non-noble metal electrocatalysts anchored on carbon cloth. It is worth mentioning that the hierarchical sea urchin-like structure promotes the redistribution of electrons and provides more catalytic active sites. This strategy shows a way for the construction of inexpensive non-noble metal electrocatalysts in the future.     

核壳结构Ru@PtRu纳米花电催化剂的制备及碱性氢析出反应性能研究

本文通过分步还原Ru、Pt前驱体,制备了以Ru为核、PtRu合金为壳的Ru@Pt_0.24Ru纳米花电催化剂,其平均直径为16.5±4.0 nm. 利用高分辨电子显微镜、电感耦合等离子体原子发射光谱和X射线光电子能谱等表征了这种电催化剂的结构和组成. 在1 mol·L ^-1 KOH水溶液中,核壳结构Ru@Pt_0.24Ru/C纳米花氢析出反应的过电位为22 mV（@10 mA·cm ^-2）,耐久性测试后过电位增加至30 mV（@10 mA·cm ^-2）,明显优于商业Pt/C电催化剂（初始值：60 mV@10 mA·cm ^-2,耐久性测试后：85 mV@10mA·cm ^-2）. 显著提高的电化学活性可能源于核壳结构Ru@Pt_0.24Ru纳米花的电子效应和几何效应,耐久性的改善可能源于核壳结构Ru@Pt_0.24Ru纳米花结构的稳定性.     

Quantitative studies on furfural and organic acid formation during hydrothermal,acidic and alkaline degradation ofD-xylose

Summary Chromatographic analysis of the degradation ofD-xylose either in plain water or aqueous sulfuric acid at temperatures ranging from 180 – 220°C gave up to 50 mol% of furfural. Activation energies did not differ significantly between reactions in plain water (E _a =119.4 kJ/mol), 0.001M H₂SO₄ (E _a =120.6 kJ/mol), 0.01M H₂SO₄ (E _a =130.8 kJ/mol), and 0.1M H₂SO₄ (E _a =120.7 kJ/mol). However, under alkaline conditions the activation energy was only 63.7 kJ/mol, indicating a different reaction mechanism. Isotachophoretic analyses revealed the formation of pyruvic, formic, glycolic, lactic, and acetic acid. While the relative yields of these acids ranged from 0.8 to 7% under hydrothermal and acidic conditions, 10 – 23% were obtained in alkaline degradation.

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Quantitative Studien zur Bildung von Furfural und organischen Säuren während des hydrothermalen, sauren und alkalischen Abbaues vonD-Xylose

Zusammenfassung Die chromatographische Analyse des Abbaues vonD-Xylose in reinem Wasser und Schwefelsäure bei Temperaturen von 180 – 220°C ergab die Bildung von bis zu 50 mol% Furfural. In bezug auf die Aktivierungsenergie zeigten sich keine signifikanten Unterschiede zwischen dem Abbau vonD-Xylose in reinem Wasser (E _a =119.4 kJ/mol), 0.001M H₂SO₄ (E _a =120.6 kJ/mol), 0.01M H₂SO₄ (E _a =130.8 kJ/mol), and 0.1M H₂SO₄ (E _a =120.7 kJ/mol). Unter alkalischen Bedingungen hingegen betrug die Aktivierungsenergie nur 63.7 kJ/mol. Dies weist auf einen unterschiedlichen Reaktionsmechanismus hin. Ferner konnte mittels Isotachophorese die Bildung von Brenztraubensäure, Ameisensäure, Glycolsäure, Milchsäure und Essigsäure nachgewiesen werden. Während sich die relativen Ausbeuten in Wasser und Schwefelsäure zwischen 0.8 und 7% bewegten, betrugen sie unter alkalischen Bedingungen 10 bis 23%.

     

Adsorptive Stripping Square-Wave Voltammetry of Creatine

ABSTRACT

An adsorptive stripping square-wave voltammetric method for quantitative determination of creatine is developed. The basic redox properties of creatine are investigated by means of square-wave and cyclic staircase voltammetry. Creatine undergoes an irreversible reduction in neutral and acidic medium at a hanging mercury drop electrode. The square-wave voltammetric response of creatine depends on the parameters of the SW excitation signal as well as on the concentration and type of the supporting electrolyte, the accumulation time and the potential and pH of the medium. The optimal experimental conditions for quantitative determination of creatine are as follows: supporting electrolyte 0.1 mol/L KNO₃ buffered with 0.1 mol/L acetate buffer to pH = 4 and accumulation potential -1.2 V. The optimal SW parameters found are: frequency f = 120 Hz, amplitude E _sw = 30 mV, and scan increment dE = 4 mV. A detection limit of 6.6 x 10^?8 mol/L creatine was obtained after 30 s preconcentration period at accumulation potential -1.2 V. The correlation coefficients of the calibration curves at concentration levels of 10^?7 to 10^?5 mol/L creatine are greater than 0.99. The results of recovery tests range from 92.18% to 102.51%.     

由碳酸钠诱导形成的油酸钠蠕虫状胶束的流变学性质

当Na₂CO₃浓度逐渐增加时, 用流变学的方法研究了阴离子表面活性剂油酸钠(NaOA)在溶液中从胶束转变成蠕虫状胶束的过程. 首先测量体系剪切粘度(η)和剪切速率的关系得到零剪切粘度(η₀). 然后由动态振荡实验得到复合粘度(|η^*|)、动态模量(储能模量G'、损耗模量G"和结构松弛时间τ_s)等物理量. 应用Cox-Merz规则和Cole-Cole图, 证明NaOA (0.040～0.080 mol/L)/Na₂CO₃ (0.25～0.50 mol/L)体系形成蠕虫状胶束, 且蠕虫状胶束的动态粘弹性在NaOA (0.050～0.080 mol/L)/Na₂CO₃ (0.35～0.45 mol/L)范围是符合Maxwell模型的线性粘弹性流体.     

Ru Nanoparticles Supported on Co-Embedded N-Doped Carbon Nanotubes as Efficient Electrocatalysts for Hydrogen Evolution in Basic Media

A challenging but urgent task is to construct efficient and robust hydrogen evolution reaction(HER) electrocatalysts for practically feasible and sustainable hydrogen production through alkaline water electrolysis. Herein we report a simple and mild pyrolysis method to synthesize the efficient Ru nanoparticles(NPs) supported on Co-embedded N-doped carbon nanotubes(Ru/Co-NCNTs) catalyst for HER in basic media. The Ru/Co-NCNTs display remarkable performance with a low overpotential of only 35 mV at 10 mA/cm², a small Tafel slope(36 mV/dec), and a high mass activity in 1 mol/L KOH, which is superior to commercial 20% Pt/C catalyst. This excellent performance is benefited from the enhanced conductivity of N-doped carbon nanotubes(NCNTs) and high intrinsic activity triggered by synergistic coupling between Ru NPs and Co-embedded N-doped carbon nanotubes(Co-NCNTs).     

Binding,Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu₂(μ,η¹ : η¹-MeCN)][X]₂ (X=weakly coordinating anion, NTf₂ ( 1 a ), FAl[OC₆F₁₀(C₆F₅)]₃ ( 1 b ), Al[OC(CF₃)₃]₄ ( 1 c )) was replaced by white phosphorus (P₄) or yellow arsenic (As₄) to yield [(DPFN)Cu₂(μ,η² : η²-E₄)][X]₂ (E=P ( 2 a – c ), As ( 3 a – c )). The molecular structures in the solid state reveal novel coordination modes for E₄ tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E₄ tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E₄ tetrahedra with release of P₄ or As₄ and formation of [(DPFN)Cu₂(μ,η¹ : η¹-^MeNHC)][X]₂ ( 4 a,b ) or to an opening of one E−E bond leading to an unusual E₄ butterfly structural motif in [(DPFN)Cu₂(μ,η¹ : η¹-E₄^DippNHC)][X]₂ (E=P ( 5 a,b ), E=As ( 6 )). With a cyclic alkyl amino carbene (^EtCAAC), cleavage of two As−As bonds was observed to give two isomers of [(DPFN)Cu₂(μ,η² : η²-As₄^EtCAAC)][X]₂ ( 7 a,b ) with an unusual As₄-triangle+1 unit.     

铁氧化还原蛋白在多壁碳纳米管上的固定、表征及直接电子转移

将来源于Spinacia Oleracea的铁氧化还原蛋白(ferredoxin, SOFd)固定在多壁碳纳米管(CNT)表面, 紫外-可见及红外光谱表明, SOFd在CNT表面没有变性, 仍保持原来的二级空间结构. 循环伏安结果表明, SOFd在CNT表面能进行有效和稳定的直接电子转移反应, 伏安曲线上出现一对良好的、几乎对称的氧化还原峰, 式量电位E^0'为(－570.4±1.5) mV (vs. SCE, 0.1 mol/L磷酸盐缓冲液), 且不随扫速和溶液pH值的变化而变化. SOFd直接电子转移的表观速率常数k_s为(0.73±0.04) s^－1.